This invention pertains to a starter generator for an internal combustion engine (an internal combustion engine starting motor and generator apparatus) serving as a starter motor when the internal combustion engine should start and as a generator after the engine starts.
There has been provided in an internal combustion engine a generator for driving various car electric devices. A conventional generator for an internal combustion engine comprises a flywheel magnet rotor mounted on a crankshaft of the engine and a stator having armature coils wound on an armature core. The stator is provided with various generator coils for driving various car electric devices necessary for driving the engine such as an ignition system for the internal combustion engine, a fuel injection apparatus and so on and a generator coil for supplying an electric power for driving arbitrarily driven loads such as lamp loads, a battery and so on.
A ring gear is secured onto an outer peripheral wall of the flywheel of the flywheel magnet rotor and a starter motor (an engine starting motor) is mounted on an engine case. A pinion gear is mounted on an output shaft of the starter motor. The pinion gear is adapted to be moved in a forward direction when the starter motor is driven and meshed with the ring gear so that the flywheel magnet rotor rotates together with the crankshaft.
Thus, as the magnet rotor rotates, a voltage is induced across the igniting generator coil provided in the stator, which causes the ignition system for the internal combustion engine to ignite the engine so that the engine starts.
Since the conventional internal combustion engine is required to have the starter and the ring gear provided on the outer peripheral face of the flywheel for starting the engine as aforementioned, the engine cannot be avoided from having a complicated construction.
As disclosed in JP58-63085, there has been proposed a starter generator that comprises an electric rotary machine having a rotor mounted on a crankshaft of an internal combustion engine and serving as an electric motor for starting the engine and as a generator after the engine starts.
However, since the starter motor (the engine starting motor) and the battery charging generator have a different winding specification necessary for meeting the characteristics required for the starter motor and the battery charging generator, respectively, the single electric rotary machine cannot be practically used as both of the starter motor and the generator even though it may be established as an idea.
More particularly, since the starter motor is required to produce a high torque when the engine should start, the generator can be also used as the starter motor as long as it should have a smaller winding resistance of the armature coils which is required for momentarily passing a larger current when the engine should start. This requires a smaller number of turns of the armature coils and a thicker diameter of the coil conductor for using the generator as the starter motor.
Since the generator is required to charge the battery with the output thereof after the engine starts, the number of turns of the armature coils should be so set that the generation output thereof around the idling revolution of the engine is substantially equal to the battery voltage.
However, with the generator for the internal combustion engine constructed in this manner, the battery is possibly damaged because the charging current for the battery is too large when the engine rotates at middle or high speed.
It will be considered that in order to prevent the battery from being over-charged a regulator is provided for shorting the output of the generator when the voltage applied across the battery gets excessive. However, with the generator having the winding resistance set to be smaller as aforementioned and the short-circuit type regulator used in combination, electronic parts for the regulator will be possibly broken due to the excessive short current.
As disclosed in JUM (Utility Model) 3-91064, there has been well known a starter generator that comprises a stator having a commutator connected to armature coils and a magnet rotor having a brush engaging the commutator in a sliding manner. The starter generator is operated as a DC motor with a brush while engaging the brush with the commutator when the engine should start and as a generator by moving the brush away from the commutator by a centrifugal clutch mechanism after the engine starts.
Such a starter generator can produce an enough starting torque by supplying the drive current to all the armature coils of the stator when the engine should start and can prevent the battery from being over-charged by supplying the output taken out from some of the armature coils through a rectifier after the engine starts.
However, since the starter generator is required to have the centrifugal clutch mechanism provided for moving the brush away from the commutator after the engine starts, the construction of the starter generator is complicated, which causes the cost to be inevitably expensive. Also, the brush and the commutator are consumed due to the engagement of the brush with the commutator when the engine should start and therefore the maintenance will be required.
Accordingly, it is a principal object of the invention to provide a starter generator for an internal combustion engine adapted to produce a high torque required to start the internal combustion engine when it should be used as a starter motor and to restrain an output thereof when it should be used as a generator so that the battery is prevented from being over-charged.
The present invention pertains to a starter generator serving as a starter motor when an internal combustion engine should start and as a generator for generating an output for charging a battery after the engine starts.
The starter generator according to the invention comprises a magnet rotor mounted on a crankshaft of the internal combustion engine, a stator, a rotor magnetic pole sensor for detecting whether the magnetic pole of the magnet rotor passing a particular position on the side of the stator is a N pole or a S pole, first through fourth switch circuits connected in parallel to both ends of the battery and a switch controller to control switch elements of the first through fourth switch circuits in accordance with the output of the rotor magnetic pole sensor.
More particularly, the magnet rotor is so constructed as to have a filed system of n poles (n is an even number of more than 4) disposed at an equal angle distance.
The stator comprises m(m=nxc3x97xcex1) coils (xcex1 is an integral number of more than 1) wound on an armature core with a winding direction identical to each other so that they are placed in order of a rotational direction of the magnet rotor and connected in series in order to each other so that they form a closed circuit and includes 1st through mth tap terminals led out from connection points between terminating ends of the 1st through mth coils and beginning ends of the coils adjacent to the 1st through mth coils so that the alternate tap terminals of the same phase among the tap terminals provide a first group of the tap terminals and the remaining alternate tap terminals of the phase reverse to those of the first group form a second group of the tap terminals.
The respective coils may be formed by winding electric conductors having a relatively larger cross section in order to pass a larger current through the coils when the internal combustion engine should start. The respective coils may have a number of turns so set that the stator can generate a voltage substantially equal to a battery voltage when the engine rotates at an idling revolution or more or less after the engine starts.
The rotor magnetic pole sensor serves to detect whether the magnetic pole of the magnet rotor passing a detection position set between particular two adjacent coils selected among the 1st through mth coils is the N pole or the S pole and to output a magnet pole detection signal of level different on the N pole and the S pole of the detected magnetic poles. The rotor magnetic pole sensor may comprise a magnetic sensor such as a hole IC to directly detect the polarity of the magnetic poles of the magnet rotor or may comprise an appropriate sensor to indirectly detect the polarity of the magnetic poles of the magnet rotor passing the position between the particular two adjacent coils of the stator. As the sensor to indirectly detect the polarity of the magnetic poles of the magnet rotor may be used a photo-encoder that comprises a photo-interrupter (a code plate) having a slit provided at a position corresponding to the magnetic pole of one polarity (N pole, for instance) of the magnet rotor and provided so as to rotate together with the magnet rotor and a luminous element and a light receiver faced each other with the photo-interrupter placed between them.
Although a general brushless DC motor has to be provided with sensors for detecting the magnetic poles of the rotor for the respective multiphase armature coils, the starter generator of the invention may be provided with just one rotor magnetic pole sensor.
The first switch circuit may comprise an upper switch element and a lower switch element connected in series to the upper switch element, an upper rectifying diode connected in parallel to the upper switch element with an anode faced to the lower switch element and a lower rectifying diode connected in parallel to the lower switch element with a cathode faced to the upper switch element. The upper switch element is connected to both ends of the battery while being faced to a positive terminal of the battery. At least one of the first switch circuits may be provided and an intermediate terminal led out between the upper and lower switch elements is connected to at least one of the tap terminals of the first group of the stator.
The second switch circuit may be constructed in the same manner as the first switch element circuit. At least one of the second switch circuits may be provided and the intermediate terminal thereof is connected to at least one of the tap terminals of the second group.
The third switch circuit may comprise an upper arm and a lower arm connected in series to the upper arm. The upper arm may comprise a series circuit of an upper switch element and an upper charge prevention diode disposed in a forward direction relative to a conduction direction of the upper switch element when it is turned on. The lower arm may comprise a lower switch element and a lower charge prevention diode disposed in a forward direction relative to a conduction direction of the lower switch element when it is turned on. The third switch circuit is connected to both ends of the battery while the upper arm is placed on the side of a positive terminal of the battery. At least one of the third switch circuits may be provided and an intermediate terminal led out between the upper and lower arms is connected to at least one of the tap terminals of the first group of the stator that is not connected to the intermediate terminal of the first switch circuit.
The fourth switch circuit may be constructed in the same manner as the third switch element circuit. At least one of the fourth switch circuits may be provided and the intermediate terminal thereof is connected to at least one of the tap terminals of the second group that is not connected to the intermediate terminal of the second switch circuit.
The switch controller to control the first through fourth switch circuits serves to control their conduction so as to turn on the upper switch elements of the first and third switch circuits and the lower switch elements of the second and fourth switch circuits when an output of the rotor magnetic pole sensor is at one of the levels and to turn on the upper switch elements of the second and fourth switch circuits and the lower switch elements of the first and third switch circuits when the output of the rotor magnetic pole sensor is at other level whereby the magnet rotor rotates in the rotational direction of the crankshaft when the internal combustion engine should start.
With the starter generator constructed in the aforementioned manner, since the larger torque can be produced by passing the drive current through all the coils of the stator when the internal combustion engine should start, the engine can start without any trouble.
After the engine starts, the charging current is supplied to the battery through a full wave rectifying circuit formed of the upper and lower rectifying diodes of the first and second switch circuits. At that time, since the output of the coils to which the third and fourth switch circuits are connected are not supplied to the battery, an excessive charging current is prevented from flowing through the battery when the engine rotates at the middle or high speed.
Although, in the aforementioned construction, the third and fourth switch circuits are provided with the charge prevention diodes for preventing the charging current from flowing through the battery, the charge prevention diodes may be omitted from the third and fourth switch circuits and the intermediate terminals led out between the upper and lower switch elements of these switch circuits may be connected to the predetermined tap terminals through tap selection switches which are controlled in accordance with the revolution of the engine so that they are at the on-state when the revolution of the engine is less than an engine start completion revolution corresponding to the one after the engine completes starting, but are at the off-state when the revolution of the engine is equal to or more than the engine start completion revolution.
In case that the starter generator is constructed in aforementioned manner, since the larger torque can be produced by passing the drive current through all the coils of the stator when the internal combustion engine should start. After the engine starts, the charging current is supplied to the battery through the full wave rectifying circuit formed of the upper and lower rectifying diodes of the first and second switch circuits, but the charging current never is never supplied to the battery through the third and fourth switch circuits. Thus, the battery can be prevented from being over-charged.